Advances in the biological, biomedical and pharmaceutical sciences have accelerated the pace of research and diagnostics to a level unparalleled to the past. With sequences of whole genome becoming available quickly and successively, the assembly of large libraries of small molecules, the ability to move pharmaceutical development, clinical diagnostic tests and basic research from a reductionist to a whole system approach quickly all demand assays that facilitate high throughput analyses. Chemiluminescence (sometimes “chemoluminescence”) is the emission of light (luminescence) with limited emission of heat as the result of a chemical reaction. Light-emitting systems have been known and isolated from many luminescent organisms, including certain bacteria, protozoa, coelenterates, mollusks, fish, millipedes, flies, fungi, worms, crustaceans, and beetles. Those enzymes isolated from beetles, particularly the fireflies of the genera Photinus, Photuris and Luciola and click beetles of genus Pyrophorus have found widespread use in reporter systems. In many of these organisms, enzymatically catalyzed oxidoreductions take place in which the free energy change is utilized to excite a molecule to a high-energy state. When the excited molecule spontaneously returns to the ground state, visible light is emitted. This emitted light is called “bioluminescence” or “chemoluminescence”. Luminescent luciferase-based assays have been developed to monitor or measure kinase activity, P450 activity, and protease activity. Firefly luciferase or click beetle luciferase catalyses the oxidation of firefly luciferin in the presence of ATP, Mg2+ and molecular oxygen with the resultant production of light. This reaction has a quantum yield of about 0.88 and this light emitting property has led to its use in luminescent assays. There are also other types of luciferin that can trigger luminescent reaction. Bacterial luciferin is a reduced riboflavin phosphate (FMNH2, pictured here), which is oxidized in association with a long-chain aldehyde, oxygen, and a bacterial luciferase. Dinoflagellate luciferin is derived from chlorophyll, and has a very similar structure. In the genus Gonyaulax, at pH 8 the molecule is “protected” from the luciferase by a “luciferin-binding protein”, but when the pH lowers to around 6, the free luciferin reacts and light is produced. Vargulin is found in the ostracod (“seed shrimp”) Vargula, and is also used by the midshipman fish Porichthys. Here there is a clear dietary link, with fish losing their ability to luminesce until they are fed with luciferin-bearing food. Coelenterazine is the most “popular” of the marine luciferins, found in a variety of phyla. This molecule can occur in luciferin-luciferase systems, and is famous for being the light emitter of the photoprotein “aequorin”. Besides enzyme-catalyzed chemoluminescence, small organic molecule based chemiluminescence assays are also widely used for analyte detection. The most important chemiluminescent compounds include luminol, acridinium and 1,2-dioxetane.